It is known to asynchronously perform writing to the frame buffer and reading of display data therefrom where the display refresh rate and the display memory (frame buffer, from now on) are configured as one set (single buffer). In this case, tearing is to occur upon each update in the case that update is in the same direction wherein those overlap in timing or that update is in directions rotated by 90 degrees.
Tearing refers to a phenomenon causing the user to perceive flickers because display different in time is made simultaneously in the upper and lower regions or in the right-side and left-side regions of the display screen because of the deviation caused between the timing of updating screen data and the timing thereof onto the display. Usually, tearing is observed as a linear form in the same direction of update where writing and reading are in an intersection at 0 degree, and as an oblique line where writing and reading are in an intersection at 90 degree.
It is disclosed by, for example JP-A-2006-98765, that a refresh rate is decided depending upon whether the image to display is a moving image or a still image in order to avoid such tearing, and that image quality is prevented from being lowered by flickers when displaying a still image content without imparting discomfort to the viewer due to tearing upon displaying a moving image content.
To avoid from tearing, frame buffers may be mounted on two surfaces (double buffer). With a double buffer, writing and reading of display data are made to and from respective, different frame buffers so that the frame buffer is switched over to output the display data upon completion of the writing.
Where display control is performed by using a double-buffer scheme, the display side perform switching of the frame buffer and reads display data therefrom after display data is completely written to the frame buffer. The time required up to display on the screen is longer as compared to the case using a single buffer. Consequently, the user possibly feels, as a depiction delay, the difference in time between user's instruction for display and actual coming into display.
In addition to the pixel density increase and vertically-oriented display of LCD screen such as the WVGA (wide video graphic array) of the mobile phone, there arise situations that, for the browser, etc., the user feels tearing and display process delay more frequently than ever upon update of the LCD screen.